The present invention relates in general to an image signal-processing apparatus based on a synthetic aperture technique, and more particularly, to an imaging apparatus which is applied to a synthetic aperture radar or an imaging system effecting the reconstruction of an acoustic image by the synthetic aperture technique.
An image signal-processing apparatus, which applies preferably to a radar or an acoustic imaging system and employs the synthetic aperture technique, emits an electromagnetic beam or an acoustic beam to an object to be detected so that the beam is irradiated with a predetermined angle and detects an image of the object based on a reflected beam from the object. Such a signal-processing apparatus has a nearly constant resolution irrespective of how far a to-be-detected area lies in the object. For this property, the signal-processing apparatus is one of the most effective apparatus in the concerned field.
For example, an imaging system using an ultrasonic beam includes a transducer which emits an ultrasonic beam that is irradiated in the vertical direction. When a to-be-detected object (regarded as a point reflector for easier explanation) is spaced vertically from the beam-emitting end of the transducer, the point reflector is horizontally scanned with the ultrasonic beam. The transducer receives an echo wave from the point reflector and transcribes it into an electrical signal which is supplied to a phase detector. The phase detector subjects the electrical signal to phase detection processing to provide analog hologram signals, which are digitized and stored in corresponding buffer memories.
The reconstruction of the image of the point reflector is carried out by the convolution integration of hologram data and the respective data of a kernel function. Actually, since the hologram data are horizontally digitized, the integration is performed by repeating a phenomenal number of multiplications and additions. Conventional imaging systems require much more time to perform the convolution integration, thus preventing faster image reconstruction.